The present invention relates to improved apparatus for centrifugally separating, cleaning or classifying solids contained in a fluid mass delivered thereto and, more particularly, to an apparatus specifically adapted for increased fiber recovery from liquid pulp suspensions. Hereinafter, such apparatus shall be referred to as a hydrocyclone cleaner and any reference individually to cleaning, separating or classifying should be construed to include a reference to cleaning, separating and classifying collectively.
Hydrocyclone cleaners are well known in the art and have been utilized for many years for separating a desired solids component, typically termed accepts, such as pulp fibers, from a liquid suspension of solids, such as a suspension of pulp in water, containing not only accepts but also undesirable solids, such as dirt, clay particles, undivided fiber bundles, commonly termed shives, and bark, typically collectively termed rejects. One very common application of hydrocyclone cleaners is the processing of wood pulp for the paper making industry wherein the separator functions to segregate the lighter and relatively less dense useable fibers within the pulp suspension from the heavier and relatively more dense unusable fibers and foreign material, collectively referred to as rejects.
In a typical hydrocyclone cleaner, the solids containing liquid suspension, also commonly referred to as a slurry, moves through the cleaner in such a manner that counter flowing vortices are established within the cleaner. A free-type vortex pattern is established along the wall of the separating chamber of the cleaner while a forced vortex flow pattern is established about the central axis of the separating chamber of the cleaner radially inward of the free-type vortex. In a typical hydrocyclone cleaner having a conical separating chamber, the outer free-type vortex pattern migrates along the wall of the conical separating chamber towards the rejects outlet which is located at the apex of the conical separating chamber, while the inner forced vortex flow pattern migrates in the reverse direction along the axis of the conical separating chamber toward the base of the conical separating chamber to an accepts outlet opening coaxially through the base of the separating chamber. Generally, an outlet tube, typically called a vortex finder, extend through the base of the hydrocyclone into the separating chamber to open thereto for capturing the forced vortex flow of accepts material and directing same out of the hydrocyclone cleaner.
The majority of the separation of solids within the pulp slurry occurs in the conical separating chamber with any heavy or relatively more dense particles in the pulp slurry migrating to the wall of the separating chamber into the outer vortex flow to pass to and through the rejects outlet at the apex of the separating chamber, while most of the liquid and the light or relatively less dense solids make a turn in the lower region of the conical separating chamber to enter the inner forced vortex and flow back through the separating chamber in a rotating flow about the central axis of the hydrocyclone cleaner to the accepts outlet. Optimally, all useable pulp fibers should exit with the accepts material through the base end of the hydrocylone and all unusable material, such as dirt and bark, with the rejects flow through the apex end of the hydrocyclone. However, in practical operation, experience has been that in the case of conventional prior art hydrocyclone separators, a significant amount of useable fibers fail to enter the inner forced vortex and are discharged with the rejects material through the apex end of the hydrocyclone. Therefore, it has become necessary and customary in the industry to repeatedly reprocess the rejects flow from the hydrocyclone cleaner in an effort to regain additional useable material.
One attempt to provide a hydrocyclone separator which would more efficiently segregate acceptable useable fibers from the unacceptable rejects material is disclosed in U.S. Pat. No. 3,347,372 which was granted to Applicant on Oct. 17, 1967, and is commonly assigned to Applicant's assignee. The hydrocyclone separator disclosed therein is characterized by an elutriating chamber which is positioned intermediate the base end and the apex end of the hydrocyclone separating chamber. The elutriating chamber comprises a cylindrical section disposed in the conical separating chamber of the hydrocyclone intermediate the base and apex ends thereof into which a flow of supplemental water is introduced by way of openings in the side of the elutriating chamber. The openings are angled towards the apex end of the hydrocyclone so as to introduce the supplemental water in such a manner that the water joins the swirling free vortex which enters the cylindrical elutriating chamber from the conical separating chamber of the hydrocyclone. The supplemental water which enters the outer free vortex of the swirling flow passing from the conical separating chamber into the elutriating chamber displaces additional useable fibers from the outer vortex to the inner forced vortex where they are carried as described previously in counterflow to the base end of the cyclone separator to exit through the vortex finder.
It is an object of the present invention to provide an improved method of separating, cleaning or classifying solids contained in a fluid mass within a hydrocyclone via the injection of supplemental fluid to the hydrocyclone.
It is a further object of the present invention to provide a hydrocyclone cleaner specifically adapted to carry out the aforementioned improved method of separating, cleaning or classifying solids in a fluid supplied to the hydrocyclone.